Recently, researches have been made on a one-chip solution that is capable of supporting multiband and low-power performance on a transmitter of a wireless communication system.
Generally, a transmitter of a wireless communication system uses a super-heterodyne system. Since the super-heterodyne system uses at least one IF, it has a complicated hardware and also requires high power consumption.
Transmitters have been proposed adopting a direct conversion system and a digital IF system which do not use an analog IF.
A transmitter using a direct conversion system may shift a phase of a Radio Frequency (RF) signal to 90 degrees because a local frequency oscillator directly generates an In-phase (I) signal and a Quadrature (Q) signal. Due to the 90-degree phase shift of the RF signal, hardware becomes complicated, power consumption increases, and modulation performance may be deteriorated.
A transmitter using a digital IF system includes a system using an I path and a Q path and a system using a single path. The former may apply a D/A converter and a low-pass filter to the I path and the Q path respectively, and may have limitations in that it is difficult to match the I path with the Q path and to generate a local RF. The latter may require a band-pass filter for RF for extracting only a single-side band RF.